Signal processing system for achilles tendon reflex testing

ABSTRACT

A signal processing system for Achilles tendon reflex testing operative to determine the elapsed time between a hammer tap and the one half relaxation point for both normal and abnormal Achilles tendon reflexes. The test operator is provided with a visual indication of foot motion which is marked to indicate the points of tap initiation and one half relaxation. A digital count is provided corresponding to each one half relaxation time and means are provided to enable entry of this data into a data processor by the test operator when a proper Achilles response has been noted.

United States Patent 1 91 1111 3,734,082 Rawson et al. [451 May 22, 1973[54] SIGNAL PROCESSING SYSTEM FOR OTHER PUBLICATIONS ACHILLES TENDONREFLEX TESTING IEEE Transactions on Bio-Med. Engineering, Oct. [75]Inventors: Edward B. Rawson, Lincoln; David 1971, pp. 353-355.

J. ORiorden, Jr., Billerica, both of The New England Journ. Of Med, May14, 1959, pp.

Mass. 1027-1028. Assigneez Searle Medidata Inc. w The New England Journ.Of Med.., 16, Pp.

Mass 761-764.

[ Filed? 1971 Primary Examiner-Kyle L. Howell] [21] APPL No: 127,555Attorney-Weingarten, Maxham & Schurgin [57] ABSTRACT [52] U.S. CI..128/2 N, 307/232, 307/25 I,

323 110 323 50 A signal processing system for Achilles tendon reflex s 1Int. Cl. ..A6lb 5/16 testing operative to determine the elapsed time[58] Field of Search ..l28/2 N, 2 s, 2 R, between a hammer p and the onehalf relaxation 128/206 A, 2.06 R, 2.1 B; 324/77 R; point for bothnormal and abnormal Achilles tendon 328/150, 1 10; 307/232, 251reflexes. The test operator is provided with a visual indication of footmotion which is marked to indicate [56] References Cited the points oftap initiation and one half relaxation. A digital count is providedcorresponding to each one UNITED STATES PATENTS half relaxation time andmeans are provided to enable 3,598,110 8/1971 Edmark ..128/2.06A entryof this data into a data Processor y the test 3,267,933 8/1966 Millseta] ..128/2.06A operator when a proper Achilles response has been3,322,115 5/1967 Richards ..l28/2N noted,

3,200,814 8/1965 Tayloretal. ..l28/2N 7 3,123,768 3/1964 Burch eta]..128/2.1B 14 Claims, 12 Drawing; Figures 62 ea Hz m GEN.

2 R ,56 so 64 A HALF RELAXATION 5 i m DETECTOR {5, LOP R 4111 count :Q INON RETRIGGERING 4 51 4 am COUNTER MULTIVIBRATOR N W 7o l 1 3rd PULSEDELAY CKT 46 44 38 40 A AMPLIFYING m CLOCK 4a 2%; DIFFERENTIATOR 79610o] unable I I06 104 L 102 l OPERATOR RECORDER CONTROL DRIVER RECORDERSIGNAL PROCESSING SYSTEM FOR ACI-IILLES TENDON REFLEX TESTING FIELD OFTHE INVENTION This invention relates to systems for timing the responseof the human body to external stimuli and in particular to a signalprocessing system for determining the one half relaxation time inAchilles tendon testing.

BACKGROUND OF THE INVENTION Recent medical research has uncovered astrong correlation between thyroid disorders of the human body andabnormal Achilles tendon reflex reactions. This discovery has enabledthyroid condition testing in a manner far more rapid and less complexthan the previously practiced clinical biochemical analysis.

The Achilles tendon reflex is normally measured by detecting theduration of foot motion in response to a tap on the Achilles tendon by apercussion hammer. Foot motion can be electrically detected from theoutput of a photodetector which receives a light beam that is variablyoccluded by induced foot motion. A display of the detector signalwaveform on a strip recorder can then be manually measured with a rulerto determine the time between hammer tap and one half relaxation of theAchilles tendon. This system of measurement is unsatisfactory forseveral reasons including the time consumed in making the measurementfrom the chart, the inaccuracy of making a measurement manually from thechart, and the inaccuracy of the displayed waveform due to phase andtime distortion inherent in electromechanical recorders.

A more satisfactory system is to provide processing electronics for thedetector signal waveform to accurately and consistently detect the timeinterval between the hammer tap and the one half relaxation point. Whilesystems are known which provide a digital indication representative ofthe elapsed time between specified points on a waveform, specialproblems exist in the field of Achilles tendon reflex testing thatrequire imaginative nd novel solutions in order to provide an accuratemeasure of the half relaxation time. For example, even with an idealnormal patient it has been found that not every Achilles tendon reflexis representative of that patients normal reflex. In particular, thefirst reflex reaction in any test is likely to be the result of initialmuscle and nerve tension which disappears in later reflexes.Additionally, many patients do not exhibit a typical normal waveformfrom an Achilles tendon reflex, but instead create waveforms havingvarying amplitudes, or which are the result of additional spastic footjerks To be useful for semi-automated Achilles tendon reflex testing, adetector signal processor must automatically account for normal andabnormal patients and the corresponding waveform responses they generateduring Achilles tendon testing.

BRIEF SUMMARY OF THE INVENTION Illustrative of the invention, anAchilles tendon reflex testing system is provided to determine anaccurate and representative elapsed time interval between hammer tap andone half muscle relaxation for the Achilles tendon reflex of normal aswell as abnormal patients. The testing system provides the test operatorwith a visual display of an electrical waveform representing foot motionduring tendon reflex and a digital indication of elapsed time betweenhammer tap and one half relaxation. Additionally, points of hammer tapand one half relaxation are marked on the displayed waveform. The testoperator can thereby determine when, with the system properly operating,an accurately representative reflex for that patient has occurred andcan accordingly cause the corresponding digital indication of elapsedtime to be recorded for use by a central processing unit as thatpatients characteristic Achilles tendon reflex time.

The normal detector waveform for Achilles tendon response comprises aninitial relatively small lobe representative of momentum exchangedbetween the hammer and the foot and a subsequent relatively longer andlarger lobe representative of tendon contraction and relaxation.Abnormal responses include those, in which the relative amplitudes ofthe two lobes are more nearly the same or even in inverse relationship,and reactions where spastic foot jerking produces additional lobes inthe detector signal waveform or where a motion is encountered directlyafter the initial two. Moreover, initial and terminal foot positionsdirectly before and after a tendon reflex are subject to substantialvariation.

Within the system according to the invention, electronics are providedto discriminate against detection of erroneous half relaxation times,when abnormal or unusual patient responses are encountered, to insurethat the time interval is accurately a measurement of the time betweenhamjrner tap and an accurate, repeatably defined one half relaxation inthe Achilles tendon muscle itself.

BRIEF DESCRIPTION OF THE DRAWINGS A more complete understanding of thepresent invention will be obtained by reference to the followingdetailed description of a preferred embodiment, presented for purposesof illustration and not by way of limitation, and by reference to theaccompanying drawings, in which:

FIG. 1 is a prior art schematic and top view of a photo-detectorarrangement for detecting patient foot motion during Achilles tendonreflex testing;

FIGS. 2A-I are waveforms of various Achilles tendon reflex responses andwaveforms at various points in the system useful in understandingoperation of the invention;

FIG. 3 is a block diagram of an Achilles tendon testing system accordingto the invention for processing the detector signals produced by footmotion; and

FIG. 4 is a partial block and partial schematic diagram of a halfrelaxation point detector operative in the circuitry of FIG. 3.

DETAILED DESCRIPTION Referring to FIG. 1 of the drawings, there is shownin top view the leg 12 of a patient supported by a stool 14 such thatthe foot 16 overhangs the stool 14 with the Achilles tendon region 18facing upward for easy reflex testing by tapping with a percussionhammer. As prior art, a light source20 provides a beam of illumination22 onto an illumination detector 24 having collimator slits 26. Thepatients foot 16 is placed to intercept the illumination 22 and toocclude a portion of the beam between the source 20 and detector 24. Anexemplary prior art photodetection system using this principle is themodel FM-l Photomotograph, Burdick Corpora tion, Milton, Wis.

Striking the Achilles tendon 18 with a percussion hammer causes the footI6 to jerk with a motion that varies the occluded portion of theillumination 22 and produces a corresponding electrical output from thedetector 24, as indicated in FIG. 2A for the case of a normal Achillesreflex. The FIG. 2A waveform comprises a first occurring lobe 28normally produced by momentum exchanged between the percussion hammerand the foot. A subsequent lobe 30 of significantly larger amplitude isthe result of the Achilles tendon reflex and comprises a rising portion30a of muscle contraction and falling portion 30b of muscle relaxation.

For purposes of identification, other portions of the curve of FIG. 2Acan be identified and include the point 28a at the beginning of curve 28where the hammer blow is first felt and the detector signal begins torise to a peak level 28b from which it falls to a minimum 280. Frompoint 28c the induced muscle contraction from the hammer tap causes therising portion 30a that reaches a peak contraction 300 from which musclerelaxation causes the falling portion 30b. A point 30d on the curve 30bis commonly referred to as the one half relaxation point and representsa level halfway between the level of points 28a and 300.

In normal Achilles tendon reflex testing, the parameter of interest isthe elapsed time between the occurrence of the point 28a and theoccurrence of the point 30d. The point of half relaxation 30d is chosento represent reflex duration because of the relative steepness of thedetector curve at that point which minimizes the time errorcorresponding to amplitude error. The one half relaxation point isdefined in terms of the initial level 28a and peak contraction level 30cbecause of uncertainty in signal level after complete relaxation.

While the response signal of FIG. 2A is the normal detector signal forthe Achilles tendon reflex response of most persons, importantvariations in this normal curve are found among patients and must beadapted to by any system used to determine the one half relaxation time.In particular, FIG. 2B shows a detector signal in which momentum andcontraction lobes of the response, 28 and 30 respectively, are of moreequal amplitude, and, in fact, it is possible to have the momentum lobe28' exceed in amplitude the contraction lobe 30. In FIG. 2C a detectorsignal is shown wherein momentum and contraction lobes, 28" and 30"respectively, have normal amplitude levels but have additional spasticcontraction lobes 32 occurring between them. In FIG. 2D a normal curveis again shown composed of momentum and contraction lobes 28" and 30"but having a trailing response lobe 34 directly following the relaxationportion of lobe curve 30". In the case of all the detector signalsindicated by FIGS. 2A-2D, the point of one half relaxation is defined bythe signal level midway between the initial and peak contraction signallevels and it is important to be able to measure the relaxation time interms of those same signal levels.

Referring now to FIG. 3, this is accomplished by a novel Achilles tendontesting system adapted for measuring the interval between the hammer tapand one half relaxation of an Achilles tendon reflex. A detector 36receives varying degrees ofillumination corresponding to reflex motionof a patients foot and provides a photoelectric detector output signalto an amplifier 38 which boosts the photoelectric signal level to adegree compatible with later processing electronics. A differentialinput is employed by the amplifier 38 to minimize common mode noise. Alow-pass filter 40 receives the output signal of the amplifier 38 and istuned to substantially reduce or eliminate Hz variations in theamplified photoelectric signal attributable to ambient light in theAchilles tendon testing area. The lowpass filter 40 eliminates thepotential for erroneous signal generation by other circuitry in thesystem in response to photodetection of ambient light in brightlylighted locations.

The output of the low-pass filter 40 is fed to both a half relaxationdetector 42 and an amplifying differentiator 44. The amplifyingdifferentiator 44 provides amplification and differentiation andproduces, from a Schmitt trigger output stage, a two level output signalwith the first level provided in response to a change in the slope ofthe filtered photoelectric signal from a zero to a positive slope, andwith the second level provided by a change in the slope of the filteredphotoelectric signal from a zero to a negative slope. A representativetwo level signal is indicated by FIG. 2E. The magnitude of the positiveand the negative slopes necessary to produce switching of the two leveloutput signal from the differentiator 44 is determined by theamplification of the differentiator 44 and hysterisis of the Schmitttrigger output stage, and is adjusted, insofar as possible, to excludeswitching on unwanted signals and noise. The two level signal from thedifferentiator 44 is fed through a gate 46 to a clock generator 48 whichoutputs a pulse of a single polarity in response to each transition inthe two level signal from the amplifying differentiator 44.

In the case of a normal photoelectric signal, such as that shown in FIG.2A, the clock generator 48 will produce a sequence of four pulsescorresponding to the points 28a, 28b, 28c, and 300 in FIG. 2A. Theoutput from the amplifying differentiator 44 is shown in FIG. 2E, andthe corresponding pulse output is shown in FIG. 2F as modified bycircuitry described below.

The normal sequence of four pulses for an Archilles reflex provided bythe clock generator 48 is fed to a four bit counter 50 through a gate 51to provide one bit advances in the count thereof with each pulse. Thecounter 50 thus provides signals indicating which pulse in the normalsequence of four pulses has most recently occurred with this indicationused for controlling other operations of the system.

In order to avoid the production of six, eight or more pulses for eachAchilles reflex in the case of the spastic contractions of FIG. 2C, athird pulse delay circuit 52 is provided which receives from the counter50 an indication of the occurrence of the second pulse corresponding tothe point 28b in FIG. 2A. A timed interval is thereby initiated toprovide an inhibit signal, shown in FIG. 20, which is fed to the gate46. This inhibit signal blocks passage of the third level transitionfrom the amplifying differentiator 44 to the clock generator 48 for apredetermined delay. All further level shifts from the amplifyingdifferentiator 44 reinitiate the delay interval of the circuit 52 whilethe delay interval is in progress. Once the predetermined delay intervalhas elapsed from the last transition, the two level output of theamplifying differentiator 44 is fed to the clock generator 48 to producethe corresponding third pulse in the four pulse sequence from thetransition of the output of the gate 46, if the output of thedifferentiator 44 is in the first state, or when that output undergoes atransition to the first state. In this manner the third pulse delaycircuit operates to discriminate between normal contraction signals 30and substantially shorter spastic contractions 32 which are of aduration insufficient to maintain the output of the amplifyingdifferentiator 44 in the one state for the length of delay interval ofthe delay circuit 52.

The pulse output of the clock generator 48 is also fed into a SET inputof an R-S flip-flop to provide an enable signal at the output thereof.The output of the flipflop 56 is fed to a gate 60 as a control for a 1KHz pulse output from a generator 62, the l KHz signal being fed intothe gate 60. The output of the gate 60 is fed to a displaying counter 64with the digital count signal from the counter 64 fed through an entrycommand terminal 66 to a computer or data processor 68. The enableoutput from the flip-flop 56 allows 1.0 KHz rate pulses from thegenerator 62 to pass to the counter 64. Alternatively, sufficientaccuracy is possible with a 100 Hz rate generator 62 instead of 1.0 KHz.

Resetting of the flip-flop 56 removes the enable signal from its outputand is accomplished in several ways. Normally, resetting of theflip-flop 56 is achieved by a signal from the half relaxation detector42 through a gate 69 upon detection of the one half relaxation point 30din a normal Achilles response detector signal of the type shown in FIG.2A or of corresponding points on the curves of FIGS. 2B-2D. The gate 69receives the indication of the fourth pulse from the counter 50 andenables passage of the output of the relaxation detector 42 only afterthis fourth pulse so as to prevent resetting of the flip-flop 56 exceptalong the signal portion 30b. A further reset for the flip-flop 56 isprovided by a nonretriggering delay timing multivibrator 70 operating ina monostable mode. The multivibrator 70 is triggered on for a selectedperiod of time by the first pulse in the four pulse sequence from theclock generator 48. This pulse is identified by a one state input to themultivibrator 70 from the counter 50. Upon detection of this first pulsethe delay timing multivibrator 70 initiates a timing interval, as shownin FIG. 2I-I, which is long relative to the duration of the normalAchilles reflex reaction. The non-retriggering delay multivibrator 70 istriggered only once on the occurrence of the first pulse from the clockgenerator 48 is a normal four pulse sequence and its timing interval isnot affected by subsequent pulses received by it. At the end of thisperiod the multivibrator 70 outputs a signal to the flip-flop 56 toreset the flip-flop 56 if it has not already been reset by the halfrelaxation detector 42. A signal from the multivibrator 70 also resetsthe four bit counter 50 to a no pulse count after the timing interval.

The function of the multivibrator 70 further includes preventing themistaken detection of a subsequent contraction signal 34, indicated inFIG. 2D, as an initial foot response portion 28. Since the normalAchilles reflex lasts substantially less than a second the timinginterval of the delay timing multivibrator 70 can be set significantlylonger than this interval and still be short enough to provide reset ofthe system before a subsequent hammer tap would be administered by thetest operator in the normal test.

The structure and operation of the half relaxation detector 42 can bestbe understood by referring to FIG. 4. The output of the low-pass filteris fed into the detector 42 through a capacitor 72 and into the input ofa unity voltage gain amplifier 74. The input of the amplifier 74 isselectively grounded through an electronic switch 76 controlled by theflip-flop 56 to provide normal grounding of the input of amplifier 74until the occurrence of the first pulse in the normal four pulsesequence sets flip-flop 56 and causes switch 76 to open. The switch 76is closed again when the flip-flop 56 is reset. When the switch 76 isopen circuited, the amplifier 74 is permitted to respond to signals fromthe capacitor 72 representing changes in the input to relaxationdetector 42 thereafter.

The output of the amplifier 74 is fed through a further capacitor 80into the input of a unity gain amplifier 82. The input of the amplifier82 is selectively grounded by a switch 84 controlled by the fourth pulseindication from the counter 50. After the end of the timing interval ofthe multivibrator 70, the counter 50 is reset and the switch 84 isplaced in a condition to ground the input of the amplifier 82. After thecounter 50 indicates the occurrence of the fourth pulse, the peakcontraction 300, the switch 84 is opened to allow the amplifier 82 torespond to the signal from the capacitor 80.

The output of the amplifiers 74 and 82 are conducted through respectiveresistors 88 and 90 to a noninverting input of a comparator 92. Aninverting input of the comparator 92 is connected to circuit ground. Theoutput from the comparator 92 provides a signal indicating the halfrelaxation point, which signal is conducted to the flip-flop 56 throughgate 69.

In the operation of the circuitry of FIG. 4, the input capacitor 72 willcharge up to the value of the detector signal prior to the occurrence ofan Achilles tendon reflex signal. At the instant that the hammer tap isadministered to the patient, the switch 76 is opened allowing theamplifier 74 to respond to the detector signal with the initial point28a of the signal established as ground. The amplifier 74 will respondby outputting a signal which charges the capacitor 80 to the level ofthe amplified, and filtered, detector signal as it varies between thepoints 28a and 30c on the curve of FIG. 2A. When the point 300 isreached, the switch 84 is opened allowing the amplifier 82 to respond tothe output of the amplifier 74 with an offset voltage provided by thecapacitor 80. This offset is equal to the signal level differencebetween the points 28a and 30c. The'outputs of the amplifiers 74 and 82then differ by an amount equal to the signal level difference betweenthe points 28a and 30c, irrespective of the value of the point 28b as inFIG. 2B. In order to identify the point in time when the photodetectorsignal, as amplified and filtered, has dropped by one half of thisdifference, the resistors 88 and 90 are chosen to be equal. The signallevel at the junction between the resistors 88 and 90 willcorrespondingly be zero, or ground, at the point when the amplified andfiltered detector signal has decreased by one half the differencebetween the initial and peak values, 28a and 300 respectively. At thispoint the comparator 92 provides a marking signal at its output which isoperative to reset the flip-flop 56 and mark the time of occurrence forthe amplifying differentiator 44. The gate 69 in FIG. 3 is provided toprevent below zero excursions of the photodetector signal between points28a and 30c from resetting the flip-flop 56.

It is alternatively possible, by simply adjusting the relative values ofthe resistors 88 and 90, to vary the point on the relaxation curve atwhich the comparator 92 provides the signal. Preferably, the one halfrelaxation point is chosen for reasons indicated above.

Returning to FIG. 3, the remaining portion of the system circuitry cannow be described and understood. The amplifying differentiator 44receives an input from the output of the flip-flop 56 which identifiesthe initial point 28a of the reflex response and the one half relaxationpoint 30d as indicated in FIG. 2A. The amplifying differentiator 44differentiates this signal from the flipflop 56 to provide respectivenegative and positive pulses which are summed with the filtered signalfrom the low-pass filter 40 and outputted to a recorder amplifier 94.Recorder amplifier 94 applies them to the pen marking control of arecorder 96 to produce the composite waveform indicated in FIG. 2]. Therecorder amplifier 94 comprises an input capacitor 98 which feeds intothe input of an amplifier 100. The input of amplifier 100 is selectivelygrounded by a logical controller 102 on the basis of an input from themultivibrator 70. The logic controller 102 provides grounding of theinput of amplifier 100 at all times except during the timing intervalproduced by multivibrator 70. The output of the amplifier 100 isconsequently operative only during an Achilles tendon reflex signal withthe signal commencing at the same D.C. level. This functioning avoidsthe problem of variations in the DC. offset of the recorder traceattributable to varying initial placement of the patients foot in thelight path between source and detector. This avoids the awkward anddifficult task of precisely placing the patients foot if offsets in therecorder trace are to be avoided.

A recorder driver 104 provides initiation of recorder operation inresponse to an input signal from an operator control 106. This signalinitiates operation and marking by the recorder 96 and provides anenable signal for the amplifying differentiator 44 a preselected timeinstant after recorder initiation to allow passage of normally blockedsignals from the amplifying differentiator to the clock generator 48.The predetermined delay in the generation of the enable signal from therecorder driver 104 allows settling of start transients from therecorder 96 to prevent them from affecting operation of the system.

While operation of the circuit has been made clear above, it isimportant to here not the cooperation of the system functions with anoperator performing the Achilles tendon testing on an actual patient.The operator has control over the system function through two points,these being the operator control 106 and the entry circuit 66. Once thepatients foot has been properly positioned to provide variation in theillumination 22, the operator initiates operation of the recorder andsystem through the operator control 106 and commences tapping on theAchilles tendon with a percussion hammer. The patient will in normalpractice be somewhat tense for the first few taps and the resultingresponses as viewed on the display of the recorder 96 will indicate thisto the operator. After a number of reflexes, however, the operator willnote from the trace on the recorder 96 that the Achilles tendon isbeginning to respond naturally and consistently for the individualpatient. After the operator sees a response on the recorder 96 whichappears representative of the response for the patient, the operator candisable further circuit operation through the operator control 106 andthen provide recording of the half relaxation time recorded in thedisplaying counter 64 into the computer 68 through operation of theentry circuit 66.

This particular cooperation between system and operator provides for ahigh degree of accuracy in the recording and entering of the one halfrelaxation interval into the computer or processor 68 where it can bemade available as part of the patients file or operated on by thecomputer in conjunction with other patient data. Of particularsignificance is the provision of both a visual, analog display at therecorder 96 and a digital time indication by the counter 64. By furtherproviding the pulses marking the points 28a and 30d on the display ofthe recorder 96, the test operator is provided with the data forevaluating each Achilles tendon reflex response to determine whetherboth patient and system are operating satisfactorily and whether thepatients reflex is a representative one suitable for providing the onehalf relaxation data.

The above description of the Achilles tendon reflex testing system hasbeen presented for purposes of illustration and accordingly thoseskilled in the art will fine alternatives and modifications to thesystem which are within the basic scope of the invention. It istherefore intended to define the scope of the invention only asindicated in the following claims.

What is claimed is:

1. In a system for testing the Achilles tendon reflex of a patient andoperative with an Achilles tendon reflex motion sensor of the typehaving an optical path between a light source and a light detector withthe optical path occluded by the foot of said patient to varying degreescorresponding to the reaction of said foot to induced reflexing of theAchilles tendon, said detector providing an output signal varying withthe degree of occlusion produced by said foot, the improvementcomprising apparatus for processing the varying detector signalincluding:

means for receiving said varying detector signal;

means for detecting first and second points on said varying detectorsignal and providing an indication of the time interval between saidfirst and second points thereon;

said first point representing the commencement of an induced Achillestendon reflex; said second point being a predetermined decay in theportion of said varying detector signal corresponding to inducedAchilles tendon reflex relaxation;

means for displaying said received, varying detector signal with anindication of said first and second points thereon.

2. In a system for testing the Achilles tendon reflex of a patient andoperative with an Achilles tendon reflex motion sensor of the typehaving an optical path between a light source and a light detector withthe optical path occluded by the foot of said patient to varying degreescorresponding to the reaction of said foot to induced reflexing of theAchilles tendon, said detector providing an output signal varying withthe degree of occlusion produced by said foot, the improvementcomprising apparatus for processing the varying detector signalincluding:

means for receiving said detector signal;

means for generating a marker signal in response to each change in saiddetector signal from a signal slope of substantially zero to a signalslope which is significantly non-zero, thereby to produce a sequence offour marker signals with each detected normal Achilles tendon reflex;

resettable means for counting said sequence of marker signals, the countthereof providing an indication of the position of each said markersignal in the sequence of marker signals; means responsive to the levelof the detector signal both prior to the occurrence of the first markersignal of said sequence and at the occurrence of the fourth markersignal of said sequence for providing a relaxation marker signal whensaid detector signal reaches a level intermediate said levels before thefirst and at the fourth marker signal;

controllable means for counting at a fixed rate in response to a startsignal and for ceasing to count in response to a stop signal;

means for producing said start signal upon the occurrence of the firstmarker signal and for producing said stop signal upon the occurrence ofsaid relaxation marker signal;

means for combining said detector signal with said first and saidrelaxation marker signals to provide a composite signal;

means for providing a visual display of said composite signal; and

means operator actuable for identifying the count in said counting meansas representing desired data for a patient Achilles tendon reflexresponse.

3. The apparatus of claim 2 further comprising:

a data processor means; and

means for conveying the count in said controllable counting means tosaid data processor means in response to an operator identificationthereof.

4. The apparatus of claim 2 further comprising:

means for causing said visual display of said composite signal tocommence at substantially the same point along the signal level axis ofsaid display. 5. Apparatus of claim 2 further comprising a low-passfilter means filtering said detector signal to provide suppression ofdetector signals resulting from ambient room lighting.

6; The apparatus of claim 2 further comprising means for inhibiting thegeneration of a first marker signal for a predetermined interval afterthe generation of a prior first marker signal, said predeterminedinterval being significantly longer than the detector signal produced byall expected Achilles tendon reflexes, thereby to prevent said firstmarker signal from being generated in response to a foot motion directlysubsequent to an Achilles tendon reflex.

7. The apparatus of claim 2 further comprising: means for producing apredetermined delay in generation of the third marker signal after thecorresponding slope change in said detector signal; and

means responsive to the running of said predetermined delay forreinitiating the running of said predetermined delay with eachoccurrence of a detector signal slope change from a zero to non-zeroslope during the running of said predetermined delay.

8. The apparatus of claim 7 wherein said means for generating saidmarker signals includes means operative to produce one of said markersignals only in response to said slope change being from said zero slopeto a non-zero slope of at least a predetermined slope magnitude.

9. The apparatus of claim 2 wherein said means for producing saidrelaxation marker signal comprises:

means for responding to changes in said detector signal to provide achange responsive signal; a first amplifier means providing a firstoutput signal; controllable means having a first state which preventspassage of said change responsive signal to said first amplifier meansand a second state which allows passage of said change responsive signalto said first amplifier means; 1

the first state of said controllable means providing conduction of theinput of said first amplifier means to a reference level;

a second amplifier means producing a second output signal;

means for storing signals which is connected between the output of saidfirst amplifier means and the input of said second amplifier means;

said signal storing means having means for providing first and secondstates, said first state providing storage of the signal between saidoutput of said first amplifier means and said reference level andfurther providing connection of said input of said second amplifiermeans to said reference level and said second state providing conductionof said first output to said input of said second amplifier means offsetby the signal stored by said storing means; means for producing a signalwith a level intermediate the level of said first and second outputs;means for producing said relaxation marker signal in response to saidintermediate signal level passing through said reference level with apredetermined slope polarity after said fourth marker signal;

said controllable means and said signal storing means being normally insaid first states;

means for changing the state of said controllable means to said secondstate in. response to the first marker signal; and

means for changing the state of said signal storing means to said secondstate in response to the fourth marker signal;

said signal storing means being thereby operative to store a signalrepresenting the difference in detector signal level between the levelprior to the first marker signal and the level at the fourth markersignal;

said intermediate signal being thereby caused to pass through saidreference level at a corresponding intermediate level of said detectorsignal.

10. The apparatus of claim 9 wherein said intermediate signal ishalf-way between the detector signal levels prior to the first markersignal and at the fourth marker signal.

11. In a system for measuring the Achilles tendon reflex of a patientoperative with an electro-optical detector providing a detector signalvarying in accordance with the movement of a foot being tested across alight beam, the improvement comprising apparatus for processing thedetector signal including:

means for amplifying said detector signal;

means for low-pass filtering said amplified signal to reduce ambientlight interference; means responsive to said filtere-d signal forproviding a two state signal;

means for producing transitions between first and second states of saidtwo state signal in response to each change in said filtered signal froma slope of substantially zero to a slope of at least a predeterminedmagnitude;

means for generating a pulse with each transition in said two statesignal whereby the detector signal of a normal Achilles tendon reflexcauses said pulse generating means to produce a sequence of four pulses;

means for indicating which pulse in said sequence of four has occurredmost recently;

means responsive to said filtered detector signal and operable onlyafter an indication of the fourth pulse in said sequence for providing amarker pulse upon the occurrence of a predetermined relaxation level ofsaid filtered detector signal after said fourth pulse;

a circuit means having two states, the first of said two states beingproduced in response to the first generated pulse in said sequence offour pulses, and the second of said two states being produced inresponse to said marker pulse;

means for counting at a predetermined rate whenever said two statecircuit is in said first state;

means responsive to said first pulse in said sequence of four pulses andsaid marker pulse to produce the second state in said two state circuita predetermined detector signal interval after said marker pulse;

means responsive to said second pulse for providing a predetermineddelay in the generation of said third pulse;

said predetermined delay being reinitiated during its running inresponse to each transition of said two state signal;

means for combining said filtered detector signal with said first pulseand said marker pulse to produce a composite signal;

means for producing a visual display of said composite signal;

a data processor means; and

means for conveying the count in said counting means to said dataprocessor means in response to a command.

12. A system for operator testing of the Achilles tendon reflex of apatient comprising:

an Achilles tendon reflex motion detector means providing an outputsignal varying with foot position;

means responsive to said varying detector signal for providing a firstsignal representing initial detector signal variation with foot motion;

means responsive to said varying detector signal for providing a secondsignal representing detector signal variation corresponding to Achillestendon reflex relaxation;

means responsive to said first and second signals for providing indiciaof the interval between said first and second signals;

means for displaying a signal representative of said varying detectorsignal; and

operator actuated means for identifying indicia corresponding to adisplayed detector signal thereby to mark acceptable indicia of Achillestendon reflex response of a patient.

13. The system for testing the Achilles tendon reflex of a patient ofclaim 12 wherein:

of a patient of claim 12 including means for preventing the providing ofsaid first signal from portions of said, varying detector signalcorresponding to foot motions directly subsequent to said tendonrelaxation.

1. In a system for testing the Achilles tendon reflex of a patient andoperative with an Achilles tendon reflex motion sensor of the typehaving An optical path between a light source and a light detector withthe optical path occluded by the foot of said patient to varying degreescorresponding to the reaction of said foot to induced reflexing of theAchilles tendon, said detector providing an output signal varying withthe degree of occlusion produced by said foot, the improvementcomprising apparatus for processing the varying detector signalincluding: means for receiving said varying detector signal; means fordetecting first and second points on said varying detector signal andproviding an indication of the time interval between said first andsecond points thereon; said first point representing the commencement ofan induced Achilles tendon reflex; said second point being apredetermined decay in the portion of said varying detector signalcorresponding to induced Achilles tendon reflex relaxation; means fordisplaying said received, varying detector signal with an indication ofsaid first and second points thereon.
 2. In a system for testing theAchilles tendon reflex of a patient and operative with an Achillestendon reflex motion sensor of the type having an optical path between alight source and a light detector with the optical path occluded by thefoot of said patient to varying degrees corresponding to the reaction ofsaid foot to induced reflexing of the Achilles tendon, said detectorproviding an output signal varying with the degree of occlusion producedby said foot, the improvement comprising apparatus for processing thevarying detector signal including: means for receiving said detectorsignal; means for generating a marker signal in response to each changein said detector signal from a signal slope of substantially zero to asignal slope which is significantly non-zero, thereby to produce asequence of four marker signals with each detected normal Achillestendon reflex; resettable means for counting said sequence of markersignals, the count thereof providing an indication of the position ofeach said marker signal in the sequence of marker signals; meansresponsive to the level of the detector signal both prior to theoccurrence of the first marker signal of said sequence and at theoccurrence of the fourth marker signal of said sequence for providing arelaxation marker signal when said detector signal reaches a levelintermediate said levels before the first and at the fourth markersignal; controllable means for counting at a fixed rate in response to astart signal and for ceasing to count in response to a stop signal;means for producing said start signal upon the occurrence of the firstmarker signal and for producing said stop signal upon the occurrence ofsaid relaxation marker signal; means for combining said detector signalwith said first and said relaxation marker signals to provide acomposite signal; means for providing a visual display of said compositesignal; and means operator actuable for identifying the count in saidcounting means as representing desired data for a patient Achillestendon reflex response.
 3. The apparatus of claim 2 further comprising:a data processor means; and means for conveying the count in saidcontrollable counting means to said data processor means in response toan operator identification thereof.
 4. The apparatus of claim 2 furthercomprising: means for causing said visual display of said compositesignal to commence at substantially the same point along the signallevel axis of said display.
 5. Apparatus of claim 2 further comprising alow-pass filter means filtering said detector signal to providesuppression of detector signals resulting from ambient room lighting. 6.The apparatus of claim 2 further comprising means for inhibiting thegeneration of a first marker signal for a predetermined interval afterthe generation of a prior first marker signal, said predeterminedinterval being significantly longer than thE detector signal produced byall expected Achilles tendon reflexes, thereby to prevent said firstmarker signal from being generated in response to a foot motion directlysubsequent to an Achilles tendon reflex.
 7. The apparatus of claim 2further comprising: means for producing a predetermined delay ingeneration of the third marker signal after the corresponding slopechange in said detector signal; and means responsive to the running ofsaid predetermined delay for reinitiating the running of saidpredetermined delay with each occurrence of a detector signal slopechange from a zero to non-zero slope during the running of saidpredetermined delay.
 8. The apparatus of claim 7 wherein said means forgenerating said marker signals includes means operative to produce oneof said marker signals only in response to said slope change being fromsaid zero slope to a non-zero slope of at least a predetermined slopemagnitude.
 9. The apparatus of claim 2 wherein said means for producingsaid relaxation marker signal comprises: means for responding to changesin said detector signal to provide a change responsive signal; a firstamplifier means providing a first output signal; controllable meanshaving a first state which prevents passage of said change responsivesignal to said first amplifier means and a second state which allowspassage of said change responsive signal to said first amplifier means;the first state of said controllable means providing conduction of theinput of said first amplifier means to a reference level; a secondamplifier means producing a second output signal; means for storingsignals which is connected between the output of said first amplifiermeans and the input of said second amplifier means; said signal storingmeans having means for providing first and second states, said firststate providing storage of the signal between said output of said firstamplifier means and said reference level and further providingconnection of said input of said second amplifier means to saidreference level and said second state providing conduction of said firstoutput to said input of said second amplifier means offset by the signalstored by said storing means; means for producing a signal with a levelintermediate the level of said first and second outputs; means forproducing said relaxation marker signal in response to said intermediatesignal level passing through said reference level with a predeterminedslope polarity after said fourth marker signal; said controllable meansand said signal storing means being normally in said first states; meansfor changing the state of said controllable means to said second statein response to the first marker signal; and means for changing the stateof said signal storing means to said second state in response to thefourth marker signal; said signal storing means being thereby operativeto store a signal representing the difference in detector signal levelbetween the level prior to the first marker signal and the level at thefourth marker signal; said intermediate signal being thereby caused topass through said reference level at a corresponding intermediate levelof said detector signal.
 10. The apparatus of claim 9 wherein saidintermediate signal is half-way between the detector signal levels priorto the first marker signal and at the fourth marker signal.
 11. In asystem for measuring the Achilles tendon reflex of a patient operativewith an electro-optical detector providing a detector signal varying inaccordance with the movement of a foot being tested across a light beam,the improvement comprising apparatus for processing the detector signalincluding: means for amplifying said detector signal; means for low-passfiltering said amplified signal to reduce ambient light interference;means responsive to said filtered signal for providing a two statesignal; means for producing transitions between first and second statesof said two state signal in response to each change in said filteredsignal from a slope of substantially zero to a slope of at least apredetermined magnitude; means for generating a pulse with eachtransition in said two state signal whereby the detector signal of anormal Achilles tendon reflex causes said pulse generating means toproduce a sequence of four pulses; means for indicating which pulse insaid sequence of four has occurred most recently; means responsive tosaid filtered detector signal and operable only after an indication ofthe fourth pulse in said sequence for providing a marker pulse upon theoccurrence of a predetermined relaxation level of said filtered detectorsignal after said fourth pulse; a circuit means having two states, thefirst of said two states being produced in response to the firstgenerated pulse in said sequence of four pulses, and the second of saidtwo states being produced in response to said marker pulse; means forcounting at a predetermined rate whenever said two state circuit is insaid first state; means responsive to said first pulse in said sequenceof four pulses and said marker pulse to produce the second state in saidtwo state circuit a predetermined detector signal interval after saidmarker pulse; means responsive to said second pulse for providing apredetermined delay in the generation of said third pulse; saidpredetermined delay being reinitiated during its running in response toeach transition of said two state signal; means for combining saidfiltered detector signal with said first pulse and said marker pulse toproduce a composite signal; means for producing a visual display of saidcomposite signal; a data processor means; and means for conveying thecount in said counting means to said data processor means in response toa command.
 12. A system for operator testing of the Achilles tendonreflex of a patient comprising: an Achilles tendon reflex motiondetector means providing an output signal varying with foot position;means responsive to said varying detector signal for providing a firstsignal representing initial detector signal variation with foot motion;means responsive to said varying detector signal for providing a secondsignal representing detector signal variation corresponding to Achillestendon reflex relaxation; means responsive to said first and secondsignals for providing indicia of the interval between said first andsecond signals; means for displaying a signal representative of saidvarying detector signal; and operator actuated means for identifyingindicia corresponding to a displayed detector signal thereby to markacceptable indicia of Achilles tendon reflex response of a patient. 13.The system for testing the Achilles tendon reflex of a patient of claim12 wherein: means are provided for determining the second maximumexcursion of said varying detector signal; said means for providing saidsecond signal includes means operative to provide said second signal inresponse to a predetermined reduction in said varying detector signalbeyond the point thereof corresponding to said determined second maximumexcursion in said varying detector signal; and said determining meansincludes means operative to discriminate against excursions of saidvarying detector signal corresponding to short, spastic foot reactionsin determining said second maximum excursion.
 14. The system for testingthe Achilles tendon reflex of a patient of claim 12 including means forpreventing the providing of said first signal from portions of said,varying detector signal corresponding to foot motions directlysubsequent to said tendon relaxation.